A response form security device is provided for use with a generally planar response form having an answer area bearing answer blanks upon which a respondent makes marks to indicate a plurality of responses. The security device includes a sleeve adapted and constructed to slidably receive and cover the response form. An access window is formed in the sleeve, and permits visual access by the respondent to a number of fewer than all of the answer areas of the response form. The length of the sleeve and the configuration of the answer window are chosen so as to prevent anyone other than the user from seeing a number of marks on the answer area sufficient to observe a repeatable pattern of marks.